Uniaxial Hot Pressing Research Articles

Remote Operated Hot Uniaxial Press to Fabricate Tc-99 bearing Ceramic Waste Forms

The objective of this senior student project is to design and build a prototype construction of a machine that simultaneously provides the proper pressure and temperature parameters to sinter ceramic powders in-situ to create pellets of rather high densities of above 90% (theoretical). This HUP (Hot Uniaxial Press) device is designed specifically to fabricate advanced ceramic Tc-99 bearing waste forms and therefore radiological barriers have been included in the system. The HUP features electronic control and feedback systems to set and monitor pressure, load, and temperature parameters. This device operates wirelessly via portable computer using Bluetootḧ technology. The HUP device is designed to fit in a standard atmosphere controlled glove box to further allow sintering under inert conditions (e.g. under Ar, He, N2). This will further allow utilizing this HUP for other potential applications, including radioactive samples, novel ceramic waste forms, advanced oxide fuels, air-sensitive samples, metallic systems, advanced powder metallurgy, diffusion experiments and more.

Microstructural and thermal investigations of HfO2 nanoparticles

Monodispersed HfO2 nanoparticles can be readily prepared at room temperature by the ammonia catalyzed hydrolysis and condensation of hafnium(IV) tert-butoxide in the presence of a surfactant. The nanoparticles are faceted with an average diameter of about 4 nm. The as-synthesized amorphous nanoparticles crystallize upon post-synthesis heat treatment. The crystallization temperature of the nanoparticles can be controlled by adjusting the annealing atmosphere. The HfO2 nanoparticles have a narrow size distribution, large specific surface area and the thermal conductivity of pressed pellets is drastically reduced compared to the bulk counterpart. The specific surface area was about 239 m2 g−1 on as-prepared samples while those annealed at 500 °C have a surface area of 221 m2 g−1 showing that the heat treatment produced no significant increase in particle size. Transmission electron microscopy (TEM) further confirmed that the nanoparticles annealed at different temperatures while X-ray diffraction studies of the crystallized nanoparticles revealed that HfO2 nanoparticles were monoclinic in structure. High density pellets of the as-synthesized HfO2 nanoparticles were obtained, using both spark plasma sintering and uniaxial hot pressing, and their thermal conductivity was measured in the temperature range from 300 to 775 K. A large reduction of the thermal conductivity was observed for HfO2 nanoparticles as compared to that of bulk HfO2. The decrease in thermal conductivity is discussed in terms of the microstructure of the compacted samples. The synthetic procedure used in this work can be readily modified for large scale production of monodispersed HfO2 nanoparticles.

Structural, optical, and scintillation characteristics of ZnO ceramics

Comprehensive studies have been carried out of the interconnection of the properties of the initial powders and characteristics of optical scintillation ZnO ceramics obtained by uniaxial hot pressing. It is established how the lattice parameters, the texture, and the transparency of the ceramic samples depend on the type of powder. The x-ray luminescence intensity of the optical scintillation ZnO ceramics, with an emission wavelength peak at 517 nm, equals about 50% of that for CsI : Tl and is comparable to that of GOS : Pr, Ce ceramic, with a mean fluorescence time of 1.0–1.6 µs. The total transmittance of 1.0-mm-thick ceramic samples is about 45% at a wavelength of 517 nm.

Finite-Element Modeling of Titanium Powder Densification

A powder-level, finite-element model is created to describe densification, as a function of applied stress during uniaxial hot pressing, of CP-Ti and Ti-6Al-4V powders with spherical or spheroidal shapes for various packing geometries. Two cases are considered: (1) isothermal densification (in the α- or β-fields of CP-Ti and in the β-field of Ti-6Al-4V) where power-law creep dominates and (2) thermal cycling densification (across the α/β-phase transformation of Ti-6Al-4V) where transformation mismatch plasticity controls deformation at low stresses. Reasonable agreement is achieved between numerical results and previously published experimental measurements and continuum modeling predictions.

Deposition of coatings containing quasicrystalline AlCuFeB and β phase by magnetron sputtering

It is known that quasicrystals show interesting material properties like a reduced surface energy, low adhesion and a low coefficient of friction. One quasicrystal which is an equilibrium phase and which is of special interest due to the low cost of the constituents is Al59Cu25.5Fe12.4B3. AlCuFeB coatings were deposited on different substrates by magnetron sputtering. All targets used were produced at the RHP-Technology GmbH by uniaxial hot pressing, using different powders. The targets show ceramic behavior like low electrical and thermal conductivity as well as high brittleness, which is probably due to the developed quasicrystalline phase. For deposition, the following parameters were varied: deposition power, working gas pressure, post annealing parameters. The deposited coatings were analyzed by high resolution scanning electron microscope (HRSEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The targets suffer from crack formation which results in statistical deviations in the coating composition and a systematic dependence of the coating composition on the working gas pressure and deposition power. It could be shown that a quasicrystalline AlCuFeB phase develops if the chemical composition is close enough to the nominal Al59Cu25.5Fe12.4B3 composition and if appropriate post annealing parameters are chosen.

Effect of vacancies on the thermoelectric properties of Mg2Si1−xSbx(0⩽x⩽0.1)

Mg${}_{2}$Si${}_{1\ensuremath{-}x}$Sb${}_{x}$ compositions with $x$ ranging from 0 to 0.1 were prepared by induction melting and compacted by hot uniaxial pressing. The lattice parameter and the positional occupancy at the Mg site as a function of Sb substitution were calculated from Rietveld refinement. A monotonic increase in the $a$lattice constant value was observed with increasing Sb substitution. Also, a decrease in the Mg site occupancy was observed with increasing Sb substitution and was confirmed by energy dispersive analysis of x-ray measurements. Room temperature carrier concentration ($n$) measurements show an increase from $1.4\ifmmode\times\else\texttimes\fi{}{10}^{18}$ cm${}^{\ensuremath{-}3}$ for $x=0$ to $1.4\ifmmode\times\else\texttimes\fi{}{10}^{20}$ cm${}^{\ensuremath{-}3}$ for $x=0.025$ followed by a nearly constant $n$, indicating the influence of vacancy formation. Electrical conductivity ($\ensuremath{\sigma}$), Seebeck coefficient ($S$), and thermal conductivity ($\ensuremath{\kappa}$) values were measured from 300 to 773 K. The observed trends in the absolute values of $\ensuremath{\sigma}$ and $S$ can be explained based on the vacancy formation at the Mg site which counteracts the doping influence of Sb. The $\ensuremath{\kappa}$${}_{L}$ (phonon component of the thermal conductivity) values show a significant decrease with increasing Sb substitution. Calculation of the thermoelectric figure of merit ($\mathit{ZT}$) shows a maximum $\mathit{ZT}$ of 0.55 for $x=0.10$ compared to a $\mathit{ZT}$ of $~$0.05 for $x=0.0$.

Effect of hot-press treatment on electrochemically deposited antimony telluride film

Antimony telluride thin film electrochemically deposited in a triethanol based alkaline electrolyte features amorphous structure, high electrical resistance, as well as fine morphology, minor impurity incorporation and anti-corrosivity. To further improve film thermoelectric performance, this film was subjected to hot-uniaxial-press (HUP) treatment at 170–250 °C. HUP treated films revealed crystallized structures, and exhibited 2–3 orders of magnitude improvement of electrical conductance. The [TeO 3 2−]/[SbO 2 −] of the deposition electrolyte was utilized to fine tune film composition and thermal electrical performance. Ni diffusion from the substrate into the film was also studied, and it can be reduced by using lower temperature and shorter time of HUP treatment. Film Seebeck coefficient and power factor reached 138 μV/K and 337 μW/K 2∙m, respectively, at elaborated deposition and HUP conditions.

Antimony Telluride Thin Films Electrodeposited in an Alkaline Electrolyte

A new alkaline electrolyte containing SbO2−, TeO32−, triethanolamine, and diaminourea polymer (DAUP) was used to deposit Sb2Tex (2 < x < 6) films. Deaeration of the electrolyte with argon was applied to eliminate oxygen interference. Hot uniaxial pressing (HUP) was chosen as the posttreatment process for the deposited films. DAUP can significantly increase the tellurium content in the deposited film, with little influence on deposition thermodynamics. The as-deposited films exhibited amorphous crystal structure. Argon deaeration proved to be favorable for improving the Seebeck coefficient of the films because oxygen contamination was reduced. HUP treatment reduced the electrical resistance of the films by orders of magnitude. The maximum Seebeck coefficient and power factor of 532 μV K−1 and 1.58 mW m−1 K−2, respectively, were obtained with DAUP and argon deaeration, followed by HUP posttreatment.

Nanoindentation hardness of hot-pressed boron suboxide

Abstract The existence of the indentation size effect implies the absence of a single hardness value for the material under investigation especially at low applied loads. In this paper we present an investigation of the indentation size dependence behaviour of nanoindentation hardness in boron suboxide ceramic compacts prepared by uniaxial hot-pressing. Berkovich nanohardness indentations were conducted and analyzed accordingly. In addition to the ordinary Oliver and Pharr method of nanoindentation data analysis, a quantitative approach for the loading curve analysis is proposed. Using the proposed approach, the description and characterization of the observed indentation size effect through the application of the Meyer’s law, and the classical and the modified proportional specimen resistance models as well as the multi-fractal scaling law was conducted and is reported. The load-independent hardness values deduced from our quantitative approach are comparable to the results calculated with conventional methods, especially with the multi-fractal scaling law.

Hydroxyapatite/diopside ceramic composites and their behaviour in simulated body fluid

In this work, diopside was introduced in hydroxyapatite matrix as a sintering aid and hydroxyapatite/diopside ceramic composites were fabricated by uniaxial hot-pressing. The biological activity of hydroxyapatite/diopside ceramic composites in simulated body fluid was assessed by means of scanning electron microscopy (SEM), thin-film X-ray diffraction (TF-XRD) and electron-probe micro analysis (EPMA). SEM micrographs showed an obvious bright mineral layer to form on the soaked composite surface, and the layer may be hydroxyapatite or NaCl crystals.

Effects of Ir Substitution and Processing Conditions on Thermoelectric Performance of p-Type Zr0.5Hf0.5Co1−x Ir x Sb0.99Sn0.01 Half-Heusler Alloys

A series of samples with the composition Zr0.5Hf0.5Co1−x Ir x Sb0.99Sn0.01 (x = 0.0 to 0.7) were synthesized by high-temperature solid-state reaction at 1173 K. High-density pellets of the powders were obtained using hot press (HP) and spark plasma sintering (SPS) techniques. The thermoelectric properties of the pellets were measured from 300 K to 750 K. Independently of the pressing conditions, all Ir-containing samples (x > 0) showed p-type semiconducting behavior. At 300 K, the electrical conductivity and thermopower of Zr0.5Hf0.5Co1−x Ir x Sb0.99Sn0.01 materials surprisingly increased with increasing Ir concentration. The largest electrical conductivity and thermopower values of 150 S/cm and 140 μV/K, respectively, were observed at 300 K for x = 0.7. The thermal conductivity of the synthesized materials decreased with increasing Ir content, went through a minimum value (x = 0.3), and increased thereafter with further addition of Ir. Pellets fabricated by SPS showed smaller thermal conductivity than pellets of the same composition obtained from uniaxial hot pressing. A thermal conductivity value of ∼2.0 W/m K was observed at 300 K for an SPS pellet with the com- position Zr0.5Hf0.5Co0.5Ir0.5Sb0.99Sn0.01. The thermal conductivity of Zr0.5Hf0.5- Co1−x Ir x Sb0.99Sn0.01 decreased with rising temperature, and the smallest value of ∼1.5 W/m K was observed at 750 K for the SPS specimen with x = 0.5.

粉末法で作製されたポーラスZn-22Al超塑性合金の異方的圧縮挙動

Closed-cell Zn-22Al alloy foams are produced through powder metallurgy process. Zn-22Al alloy powders and titanium hydride powders were mixed to prepare a precursor. The precursor was manufactured using uniaxial hot pressing. Macro- scopic porosity is as large as 70% in the condition of heating temperature at 873 K for 20 min. Average pore aspect ratio is 0.48 and the pores extended in the direction of perpendicular to hot pressing were observed. Compressive tests were carried out in the different loading axes and crosshead speeds. Plateau stress in the direction of hot pressing was lower than the direction of perpendicular to hot pressing. Anisotropic deformation behavior is due to the anisotropic cell morphology which was induced during the uniaxial hot pressing. In contrast, difference of strain rate sensitivity exponent (m value) in the compressive directions was not observed. This is because the m value does not depend on cell morphology but on cell wall material.

Analysis of the Indentation Size Effect in the Microhardness Measurements inB6O

The Vickers microhardness measurements of boron suboxide (B6O) ceramics prepared by uniaxial hot-pressing was investigated at indentation test loads in the range from 0.10 to 2.0 kgf. Results from the investigation indicate that the measured microhardness exhibits an indentation load dependence. Based on the results, we present a comprehensive model intercomparison study of indentation size effects (ISEs) in the microhardness measurements of hot-pressed B6O discussed using existing models, that is, the classical Meyer's law, Li and Bradt's proportional specimen resistance model (PSR), the modified proportional specimen resistance model (MPSR), and Carpinteri's multifractal scaling law (MFSL). The best correlation between literature-cited load-independent Vickers microhardness values, the measured values, and applied models was achieved in the case of the MPSR and the MFSL models.

A comparative study of ZnS powders sintering by Hot Uniaxial Pressing (HUP) and Spark Plasma Sintering (SPS)

The sintering of two different polycrystalline zinc sulphide powders has been investigated by two different techniques. Conventional sintering technique (Hot Uniaxial Pressing, HUP) and the Spark Plasma Sintering (SPS) also known as electric field-assisted sintering technique (FAST) have been compared in terms of sintering parameters (temperature, pressure) and optical properties of the prepared ZnS ceramics. This study demonstrates the potentiality to sinter ZnS by SPS in very short times, at lower sintering temperatures, compared with HUP, with good densification (close to the theoretical density) and good optical transmission in the infrared range 8–12 μm.

ChemInform Abstract: Effect of Hot-Pressing on the Bi-Pb-Sr-Ca-Cu-O System.

Uniaxial hot-pressing has been used to improve the relative density and preferred gain orientation of the nearly pure (Bi, Pb)2Sr2Ca2Cu3O10-y (2223) phase in the Bi-Pb-Sr-Ca-Cu-O system. Samples were prepared by freeze-drying, calcining, and hot-pressing the powders at 650° to 840°C at 50 and 200 MPa for 2 h. The hot-pressed samples showed a high degree of grain alignment and increased density up to 99% of theoretical. At 200 MPa, the 2223 phase was partially destroyed during hot-pressing, probably because of the weak bonding between the Bi─O2 layers. However, the 2223 phase and superconductivity were recovered with subsequent annealing. The critical current density (Jc) was improved 10-fold over that of sintered samples through this technique, with the highest Jc being 2100 A°Cm−2 at 77.3 K and zero field. The hot-pressed samples also showed significant improvements in the Jc as a function of applied magnetic field. The Jc of a hot-pressed and postannealed sample at 0.2 T and 77.3 K was 2 orders of magnitude greater than that of a sintered sample.

ChemInform Abstract: Mechanically Alloyed Permanent Magnets

Mechanical alloying is applied to prepare Nd-Fe-B and Sm-Fe-TM-type permanent magnets (TM: transition metals). Starting from elemental powders, the hard magnetic phases are formed by milling in a planetary ball mill and a successive solid-state reaction at relatively low temperatures. For Nd-Fe-B, the magnetically isotropic particles are microcrystalline, show a high coercivity (up to 20 kOe for ternary alloys and above for Dysubstituted samples) and can be either used for making bonded magnets or compacted to dense isotropic magnets by hot uniaxial pressing. Magnetically anisotropic samples are formed by die-upsetting. With regard to grain size, magnetic properties, compaction and formation of anisotropy, the mechanically alloyed material is comparable with rapidly quenched Nd-Fe-B. The mechanical alloying process has also been applied to prepare magnetic material of 3 new Sm-Fe-TM phases. In Sm-Fe-V with the ThMn12 crystal structure, coercivities up to 11.8 kOe, in Sm-Fe-Zr with the PuNi3 crystal structure coercivities up to 14.8 kOe and in A2-phase Sm-Fe-Ti giant coercivities up to 64 kOe (at room temperature) were achieved.

Integral, absolute, and relative light yield of ZnO-based ceramics

Zinc-oxide-based ceramics were prepared by uniaxial hot pressing and their optical properties and luminescence-scintillation characteristics (for X-ray and gamma excitation) have been studied. The ceramics exhibit 35% transmission in the region of maximum wavelength of X-ray-induced luminescence (520 nm); an absolute light yield from 10 900 to 25 360 photons/MeV (depending on the pulse formation time in a spectroscopic amplifier); energy resolution of 11.8–19.2% (for complete absorption of 662-keV gamma quanta); and linear relative yield within 2% in a 35-662 keV energy range.

Production, Kinetic Study and Properties of Fe-Based Glass and Its Composites

Fe-based glassy powders with four different compositions of varying copper content were produced by mechanical alloying of elemental powder mixtures. The thermal stability as well as the crystallization kinetics was investigated using differential scanning calorimetry in both isochronal and isothermal modes. The isochronal and isothermal activation energies have a similar value (∼560–570 kJ/mol). In addition, the Johnson–Mehl–Avrami (JMA) analysis shows that the transformation is diffusion controlled three-dimensional process, and the crystallization proceeds with increasing nucleation rate. Metal matrix composites were synthesized through powder metallurgy methods by uniaxial hot pressing and subsequent extrusion of commercially pure Fe powders, blended with Fe-glass reinforcement. The resultant properties of the composites strongly depend on the composition of the glassy reinforcement.

Compression creep studies of mechanically alloyed nanostructured Fe-12Cr-2W-0.25Y2O3 ODS alloy

Nanocrystalline Fe-12Cr-2W (wt.%) and oxide dispersion strengthened (ODS) Fe-12Cr-2W-0.25 Y2O3 (wt. %) alloy powders were produced through mechanical alloying in a high energy planetary ball mill. Microhardness studies on individual milled powder particles revealed a clear increase of hardness for the Yttria containing alloy, thus, proving the ODS effect to be operative in the powders. Consolidation was carried out in a uniaxial hot press at 900°C with a pressure of 200 MPa. TEM and XRD analyses consistently revealed the nanocrystalline grain size before (12 to 30 nm) and after consolidation (120 nm), respectively. Compression creep studies in a temperature range between 800 and 1000°C revealed that diffusional creep is obviously suppressed in these materials. However, the creep resistance of the ODS ferritic steel is only marginally higher than its base alloy and both alloys are by far less creep resistant than that of a ferritic steel of comparable baseline composition strengthened by complex and exceptionally thermally stable Ti-Y-O nanoclusters [1]. Both differences can be rationalized by the instability of the microstructure leading to significant particle and grain growth after creep testing.

Influence of hot-pressing on MgB2/Nb/Monel wires

Uniaxial hot-pressing was applied as an alternative way to further improve the grain connectivity of both un-doped and carbon doped MgB2/Nb/Monel wires. In this study, hot-pressing of 100MPa resulted in the improvement of the mass density, the critical current density, and the grain connectivity of the wires. However, this also caused additional critical current density anisotropy, which is associated with the texture of a- and b-axes oriented grains. In particular, the anisotropy factors of critical current density for the un-doped and the carbon doped conductors were estimated to be 2.6 and 1.7, respectively, under an external magnetic field of 14T.